WASHINGTON — Expanding the prostitution investigation, the Secret Service acknowledged Thursday that it is checking whether its employees hired strippers and prostitutes in advance of President Barack Obama’s visit last year to El Salvador.

The disclosure came not long after the Homeland Security secretary assured skeptical senators that the recent prostitution scandal in Colombia appeared to be an isolated incident.

A spokesman for the Secret Service, Edwin Donovan, said the agency was investigating allegations raised in news reports about unprofessional behavior that have emerged in the aftermath of the Colombia incident.

The latest, by Seattle TV station KIRO-TV, quoted anonymous sources as saying that Secret Service employees received sexual favors from strippers at a club in San Salvador and took prostitutes to their hotel rooms ahead of Obama’s visit to the city in March 2011.

Prostitution is legal in both Colombia and El Salvador.

Separately, the Washington Post this week cited unnamed “confidants” of the Secret Service officers implicated in Colombia saying senior managers had tolerated similar behavior during previous official trips. The Post described a visit to Buenos Aires in 2009 by former President Bill Clinton, whose protective detail it said included agents and uniformed officers. During that trip, the Post said, members of the detail went out for a late night of partying at strip clubs.

Donovan said Thursday, “Any information brought to our attention that can be assessed as credible will be followed up on in an appropriate manner.”

In a confidential message to senators, also Thursday, the Secret Service said its Office of Professional Responsibility had not received complaints about officer behavior in El Salvador but would investigate.

In the message, the agency sought to cast doubt on the KIRO report, noting that it does not routinely send K-9 or explosive-detection units as part of its advance teams; KIRO said the advance team included those elements.

White House spokesman Jay Carney said he doubted that Obama was aware of the allegations about El Salvador when he was briefed by Secret Service Director Mark Sullivan last week in the Oval Office.

The expansion of any investigation into behavior by the Secret Service could represent another mark against an agency that has been tarnished by the prostitution scandal.

Otto Warmbier was arrested in January 2016 at the end of a brief tourist visit to North Korea. He had been medically evacuated and was being treated at the University of Cincinnati Medical Center when he died at age 22.